Spring Driven Injection Device

ABSTRACT

The present invention relates to an injection device for automatic torsion spring driven injection of a liquid drug. The injection device is of the type wherein a telescopically movable needle shield activates the release of the torque of the torsion spring to drive the injection when the needle shield is moved from its extended position to a retracted position. The injection device further has a needle holder carrying the injection needle, which needle holder is axially movable both in relation to the housing and in relation to the needle shield. It is therefore possible to retract the needle shield in relation to the housing and at the same time move the needle holder to its extended position such that the injection needle is presented outside the needle shield thereby providing for easy exchange of the injection needle.

THE TECHNICAL FIELD OF THE INVENTION

The invention relates to a torsion spring driven injection device forinjection of multiple set doses. In particular, the invention relates toa torsion spring driven injection device of the type where the injectionneedle is shielded during injection and where the axial movement of theneedle shield releases the injection of the set dose.

DESCRIPTION OF RELATED ART

An automatic torsion spring driven injection device is disclosed in EP338,806. In one embodiment, the injection needle is covered by atelescopically movable needle shield. When the shield is pressed againstthe skin of a user, a compression spring drives the body of the penforward such that the tip of the injection needle penetrates the skin ofthe user, and a torsion spring is released to perform an injection ofthe liquid drug contained in the injection device. In such shieldtriggered injection devices, the step of pressing an injection buttonhas been eliminated and the injection needle is hidden during injection,however, exchanging the injection needle is troublesome as the userneeds to remove the needle shield in order to gain access to theinjection needle.

A different spring driven pen-shaped injection device having a shieldedinjection needle is known from U.S. Pat. No. 7,112,187. The injectiondevice disclosed is an automatic spring-driven injection in which anactuation spring provided inside the housing thrusts the piston rodforward during injection. An important characteristic of such automaticinjection device is that no element move out from the injection deviceduring dose setting. Thus, the injection device has a constant lengthduring operation. This particular injection device has a mode selectorwhich is rotated to select one out of three different modes. In one modethe shield is locked and in a different mode the shield is unlocked. Inthe unlocked position, the shield can be moved axially between anextended and a retracted position. In the retracted position a user hasaccess to the distal end of the injection device and is thus able toattach or remove an injection needle. Further, the mode selector can berotated to an injection position, in which position the set dose isreleased when the shield is moved to its retracted position duringinjection.

For automatic spring driven injection devices for multiple injections ofset doses in which the triggering of the injection is made by thebackward movement of the needle shield a particular challenge ispresent. In order to exchange the injection needle, the needle shieldneeds to be axially removed from the hub of the injection needle suchthat the user can rotate or twist the hub in order to couple or decouplethe injection needle. However, when performing the injection, the needleshield must trigger the release of the dose when only the distal part ofthe needle cannula is penetrated into the body.

In EP 338,806 this is solved by simply removing the needle shield duringchanging of the injection needle whereas in U.S. Pat. No. 7,112,187 itis done by a complicated mechanism involving a mode selector. However,in both examples it is difficult to explain the user how to handle theinjection device as the user has to perform many different steps andremember which steps in the sequence of executing the injection he orshe has fulfilled.

A further manual injection device in which the cartridge is disconnectedfrom the injection needle by axial movement of the cartridge isdescribed in WO 2011/051366.

DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a spring driveninjection device for multiple automatic injections of set doses whichare very simple to handle and which do not require any, or only verylittle, explanation to the user but wherein the working of the injectiondevice is self-explanatory.

It is particularly an object of the present invention to provide ashield triggered automatic injection device which facilitates easyexchange of the injection needle without accidentally pushing on theneedle shield during needle shift and thereby activating the injectionprocess.

The invention is defined in claim 1.

Accordingly, in one aspect of the present invention, an injection devicefor torsion spring driven injection of a liquid drug is provided.

The torsion spring driven injection device comprises:

-   -   A housing storing all the mechanical components of the injection        deivce including the cartridge containing the liquid drug. The        cartridge is axially fixated to the housing, such that the        cartridge cannot move axially in relation to the housing.    -   A dose setting arrangement for setting the size of the dose to        be injected. The dose setting arrangement includes a proximally        mounted dose setting button which the user rotates to set the        size of the dose to be injected.    -   A torque spring drive mechanism for driving the set dose out        from the cartridge. The drive mechanism includes a torsion        spring which is strained by the user when setting a dose and        released to inject the set dose. It has proven to be beneficial        if a certain amount of prestraining is preloaded into the        torsion spring such that small sizes of drug can be injected        without the spring force necessarily having to return to zero        for each individual injection. The torsion spring can        alternatively be fully preloaded when the injector is delivered        to the user such that the user does not need to strain the        torsion spring at all. The preload is thus sufficient to empty        the drug cartridge through a number of doses as in U.S. Pat. No.        7,112,187.    -   A torsion spring which applies its torque to rotate a piston rod        guide which then during its rotation moves the piston rod        axially forward to press the liquid drug out through the        injection needle mounted to the injection device.    -   A telescopically movable needle shield for covering the distal        end of the injection needle in a situation of use. The needle        shield is further adapted to release at least portion of the        torque of the torsion spring when moved axially, and    -   a needle holder for carrying the injection needle.

The needle holder is slidable mounted in the housing such that theneedle holder carrying the injection needle and the housing carrying thecartridge can be moved axially in relation to each other such that theproximal end of the injection needle can be moved into and out ofengagement with the septum of the cartridge.

In addition, the needle shield activating the injection can be movedaxially in relation to both the housing and the needle holder, wherebythe needle holder carrying the injection needle can be moved to anextended position while the shield can be moved to a retracted positionthus enabling easy exchange of the injection needle.

Firstly when an injection sequence is initiated, the needle holder is inits distal position extending out from the needle shield such that auser can exchange the injection needle.

When setting a dose, the needle shield is released to be moved into itsextended position covering the distal end of the injection needle.

When pressed against the skin, the needle shield and the needle holdermoves proximately such that the proximal end of the needle shieldpenetrates the septum of the cartridge where after the injection isautomatically performed.

When removing the shield form the surface of the skin, the shieldremains in its retracted position and the needle holder automaticallyslides forward such that the proximal end of injection needle decouplesform the septum of the cartridge and the user can once again gain accessto the injection needle.

Thus, having a housing to which the cartridge is fixed and a needleshield telescopically and axially movable in relation thereto togetherwith a needle holder which is axial movable both in relation to thehousing and to the shield provides for optimal handling of the injectionneedle. As explained the shield can be retracted and the needle holderpushed distally which presents the injection needle for manual handlingby the user.

Also since the needle holder is axial movable, the proximal end of theneedle cannula decouples instantly from the cartridge as the shield isremoved from the surface of the skin, it is therefore no longernecessary to maintain the injection needle inserted into the skin of theuser as no more drug will flow through the injection needle once thenon-patient end is removed from the septum of the cartridge. Also whenthe injection needle is decoupled, air will not be sucked into thecartridge through the lumen of the injection needle why the so-calledair-shot or flow-check usually performed prior to injection in order toremove air from the cartridge is no longer necessary.

The torsion spring is preferably encompassed between the housing and thepiston rod guide such that the piston rod guide is able to rotate underinfluence of the torsion spring. However one or more other elements canbe present between the housing and the piston rod guide. In one examplethe torsion spring might be connected to a spring base element which issecured to the housing.

Further, a rotatable drive tube for rotating the piston rod guide can bepresent. The drive tube can be connected to the torsion spring such thatthe drive tube can be rotated by the user to strain the torsion springand released to rotate the piston rod guide. This would require aratchet mechanism for holding the torque introduced into the torsionspring.

A clutch or activator coupling the drive tube to the piston rod guidewould also be recommendable. Such clutch is movable between a firstposition in which the clutch is rotational locked to the housing e.g. bya toothed interface and a second position in which the clutch isrotational released from the housing and rotational coupled to both thedrive tube and to the piston rod guide such that the torque of thetorsion spring is transferred via the drive tube to the piston rodguide. Thus, in the first position the clutch is secured to the housingwhereas the clutch in the second position is coupled to the drive tubewhich is released to rotate the piston rod guide.

The piston rod guide further engages the piston rod either via a keyedengagement or via a threaded engagement. In the first case the pistonrod guide will rotate the piston rod distally ( in this case the pistonrod is threaded to the housing). In the second case the piston rod willmove distally without rotation when the piston rod guide is rotated (inthis case the piston rod is keyed to the housing).

A helical compression spring is provided between the housing and theneedle shield urging the needle shield in the distal direction to coverthe distal end of the injection needle. However, the needle shield isengaged with the helically movable scale drum whenever the scale drum isin its zero position i.e. when no dose is set and the number “0” isdisplayed in the window displaying the set dose size.

This engagement is preferably made between hooks, indentations or thelike on the needle shield engaging cooperating hooks or the likeprovided in the scale drum.

The needle shield slides on an outside surface of the needle holder. Theneedle holder is provided with a plurality of flexible arms extendingvertically and engaging the needle shield thus preventing axial movementof the needle shield in relation to the needle holder. These arms arepreferably positioned such that the arms bend inward whenever aninjection needle is mounted onto the needle holder. When the arms arebended inwardly i.e. when an injection needle is mounted, the needleshield can slide freely on the needle holder. In this way the needleshield is prevented from moving into its extended position when noinjection needle is mounted.

When the needle shield during injection moves from its extended positionto its retracted position it moves with it the needle holder due to hookmeans provided on the needle shield and engaging the needle holder.

Since the needle holder carries the injection needle, the needle cannulais also moved in the proximal direction such that the proximal end ofthe injection needle penetrates the septum of the cartridge allowing theliquid drug in the cartridge to flow through the injection needle.

At the same time the axial and proximally movement of the needle holderactivates the release of the torsion spring to drive the drive mechanismby axially moving the clutch or activator.

During the expelling of the set dose, the scale drum rotates back to itszero position. When the scale drum at the end of the injection reachesits zero position with the number “0” showing in the window, the needleholder is released from the needle shield such that the needle holdercan move axially in the distal direction under influence of a springprovided between the needle holder and the housing.

In its zero position the scale drum abuts with a protrusion of theneedle holder to release the needle holder from the shield such that theneedle holder can slide axially in the distal direction.

In a different embodiment, the invention relates to a torsion springdriven drug delivery device of a liquid drug comprising:

-   -   A housing storing a cartridge containing the liquid drug to be        injected.    -   A needle holder to which an injection needle can be mounted,    -   A needle shield for covering the injection needle during use,        and        wherein, the needle shield is slidable relatively to the needle        holder and which needle holder is provided with a number of        flexible arms preventing axial movement of the needle shield        when no injection needle is mounted on the needle shield and        which arms are moved into alignment with the needle holder when        an injection needle is mounted on the needle holder thereby        allowing the needle shield to move axially relatively to the        needle holder.

In this way, the needle shield can only slide relatively to and on theneedle holder when an injection needle has been mounted onto the needleholder.

When no injection needle is mounted, the needle shield is preferablysecured in its proximal retracted position allowing a user to change theinjection needle, and when an injection needle is mounted and theflexible arms are pressed into alignment with the needle shield, theneedle shield can pass in its sliding movement towards its distalposition.

However, in a further embodiment of the invention, the needle shield iseither alone or in addition prevented from axial movement by engagementbetween the needle shield and the scale drum. In this furtherembodiment, the spring driven delivery device comprises:

-   -   A housing storing a cartridge containing the liquid drug to be        injected.    -   A scale drum threadely engaged with the housing to perform an        helical movement away from a zero position during setting of a        dose.    -   A needle shield for covering the injection needle during use,        which needle shield can slide axially in relation to the        housing, and        wherein the scale drum engages and locks the needle shield when        in the zero position.

Whenever the scale drum is in its zero position, i.e. the position inwhich no dose has been set, and the cipher “0” appears in the window ordisplay of the injection device, engagement means on the scale drumarrests the needle shield and secures it from axial movement.

When a user dials a dose and the scale drum moves away from its zeroposition, these engagement means releases and set the needle shield freeto move whereby the needle shield is slidable into a position in whichit covers the injection needle.

In a further embodiment of the invention, the needle shield can bebiased by a compression spring to move in the distal direction whenreleased from scale drum.

A further embodiment combines the two previous embodiments and thusrequires the user to both mount an injection needle to move the flexiblearms away from the needle shield and to set a dose to release the needleshield. When these two actions have been performed, the needle shield isslidable into its extended position covering the distal end of theinjection needle.

DEFINITIONS

An “injection pen” is typically an injection apparatus having an oblongor elongated shape somewhat like a pen for writing. Although such pensusually have a tubular cross-section, they could easily have a differentcross-section such as triangular, rectangular or square or any variationaround these geometries.

The term “Needle Cannula” is used to describe the actual conduitperforming the penetration of the skin during injection. A needlecannula is usually made from a metallic material such as e.g. stainlesssteel and connected to a hub to form a complete injection needle alsooften referred to as a “needle assembly” or simply an “injection needle”A needle cannula could however also be made from a polymeric material ora glass material. The hub also carries the connecting means forconnecting the needle assembly to an injection apparatus and is usuallymoulded from a suitable thermoplastic material. The “connection means”could as examples be a luer coupling, a bayonet coupling, a threadedconnection or any combination thereof e.g. a combination as described inEP 1,536,854.

Needle assemblies specially designed for pen injections systems aredefined in ISO standard No. 11608, part 2, and are often referred to as“pen needles”. Pen needles have a front-end for penetrating into theskin of the user and a back-end for penetrating into the cartridgecontaining the drug.

As used herein, the term “drug” is meant to encompass anydrug-containing flowable medicine capable of being passed through adelivery means such as a hollow needle in a controlled manner, such as aliquid, solution, gel or fine suspension. Representative drugs includespharmaceuticals such as peptides, proteins (e.g. insulin, insulinanalogues and C-peptide), and hormones, biologically derived or activeagents, hormonal and gene based agents, nutritional formulas and othersubstances in both solid (dispensed) or liquid form.

“Scale drum” is meant to be a cylinder shaped element carrying indiciaindicating the size of the selected dose to the user of the injectionpen. The cylinder shaped element making up the scale drum can be eithersolid or hollow. “Indicia” is meant to incorporate any kind of printingor otherwise provided symbols e.g. engraved or adhered symbols. Thesesymbols are preferably, but not exclusively, Arabian numbers from “0” to“9”. In a traditional injection pen configuration the indicia isviewable through a window provided in the housing. When reference ismade to a “zero position” of the scale drum, this does not necessarilymean that the number “0” is present, however it merely refers to theposition of the scale drum in which no dose has been set.

“Cartridge” is the term used to describe the container containing thedrug. Cartridges are usually made from glass but could also be mouldedfrom any suitable polymer. A cartridge or ampoule is preferably sealedat one end by a pierceable membrane referred to as the “septum” whichcan be pierced e.g. by the back-end of an injection needle. The oppositeend is typically closed by a plunger or piston made from rubber or asuitable polymer. The plunger or piston can be slidable moved inside thecartridge. The space between the pierceable membrane and the movableplunger holds the drug which is pressed out as the plunger decreased thevolume of the space holding the drug. However, any kind ofcontainer—rigid or flexible—can be used to contain the drug.

Since a cartridge usually has a narrower neck portion into which therubber plunger cannot be moved, not all of the drug contained inside thecartridge can be expelled. The term “initial quantum” therefore refersto the initial quantum of the injectable content. The term “remainingcontent” in the same way refers to the remaining injectable content.

Further the term defines a piercing member adapted to penetrate the skinof a subject for the purpose of delivering or removing a liquid.

Using the term “Automatic” in conjunction with injection device meansthat, the injection device is able to perform the injection without theuser of the injection device during dosing deliver the force to expelthe drug. The force is typically delivered by an electric motor or by aspring as herein described which spring is strained by the user duringdose setting. Such springs are usually prestrained in order to avoidproblems of delivering very small doses. Alternatively, the spring canbe preloaded by the manufacturer with a preload sufficient to empty thedrug cartridge though a number of doses. Typically the user activates alatch or a button on the injection device to release the forceaccumulated in the spring when carrying out the injection.

All references, including publications, patent applications, andpatents, cited herein are incorporated by reference in their entiretyand to the same extent as if each reference were individually andspecifically indicated to be incorporated by reference and were setforth in its entirety herein.

All headings and sub-headings are used herein for convenience only andshould not be constructed as limiting the invention in any way.

The use of any and all examples, or exemplary language (e.g. such as)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

The citation and incorporation of patent documents herein is done forconvenience only and does not reflect any view of the validity,patentability, and/or enforceability of such patent documents.

This invention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained more fully below in connection with apreferred embodiment and with reference to the drawings in which:

FIG. 1 show a perspective view of the injection device prior to use.

FIG. 2 show a perspective view of the injection device with the capremoved.

FIG. 3 show a perspective view of the injection device with theinjection needle mounted.

FIG. 4 show a perspective view of the injection device with the needleshield in its extended position.

FIG. 5 show a perspective view of the injection device during injection.

FIG. 6 show a perspective view of the injection following injection.

FIG. 7.1-7.8 show a schematic view of the various sequences ofperforming an injection using the injection device according to theinvention.

FIG. 8 show a cross sectional view of the injection device according toa first example.

FIG. 9 show an exploded view of the injection device in FIG. 8.

FIG. 10 show a detailed cross sectional view of the engagement betweenthe needle shield and the scale drum.

FIG. 11 show a detailed cross sectional view of the needle shieldreleased from the scale drum.

FIG. 12 show a detailed cross sectional view of the connecting means ofthe needle holder without an injection needle attached.

FIG. 13 show a detailed cross sectional view of the connecting means ofthe needle holder with an injection needle attached.

FIG. 14 show a detailed cross sectional view of the activation mechanismduring injection.

FIG. 15 show a different detailed cross sectional view of the activationmechanism.

FIG. 16 show a detailed cross sectional view of the activation mechanismupon activation.

FIG. 17 show a detailed cross sectional view of the proximal end of theinjection device.

FIG. 18 show a perspective view of the mechanism releasing the needleholder following injection.

FIG. 19 show a cross sectional view of the injection device according toa second example.

FIG. 20 show an exploded view of the injection device in FIG. 19.

FIG. 21 show a cross sectional view of the injection mechanism accordingto the FIGS. 19-20 in the non-dosing position.

FIG. 22 show a cross sectional view of the injection mechanism accordingto the FIGS. 19-20 when releasing a set dose.

FIG. 23 show a side view of the interior of the injection device of theFIGS. 19-20 with the needle holder locked to the needle shield.

FIG. 24 show a perspective view of FIG. 22.

FIG. 25 show a side view of the interior of the injection device of theFIGS. 19-20 with the needle holder released from the needle shield andthe needle shield locked to the scale drum.

FIG. 26 show a perspective view of FIG. 24.

The figures are schematic and simplified for clarity, and they just showdetails, which are essential to the understanding of the invention,while other details are left out. Throughout, the same referencenumerals are used for identical or corresponding parts.

DETAILED DESCRIPTION OF EMBODIMENT

When in the following terms as “upper” and “lower”, “right” and “left”,“horizontal” and “vertical”, “clockwise” and “counter clockwise” orsimilar relative expressions are used, these only refer to the appendedfigures and not to an actual situation of use. The shown figures areschematic representations for which reason the configuration of thedifferent structures as well as there relative dimensions are intendedto serve illustrative purposes only.

In that context it may be convenient to define that the term “distalend” in the appended figures is meant to refer to the end of theinjection device which usually carries the injection needle whereas theterm “proximal end” is meant to refer to the opposite end pointing awayfrom the injection needle and carrying the dose dial button asdepictured in the FIGS. 1 to 6.

FIG. 1 to FIG. 7 discloses a torsion spring driven injection deviceduring its different stages. The features and the working modesdisclosed in the FIGS. 1 to 7 is common for both examples.

When delivered to a user, the injection device 1 has a cap 2 secured tothe distal end of the housing 3 as disclosed in FIG. 1. Further, theinjection device 1 has a dose setting button 4 at its proximal end and awindow 5 provided in the housing 3 through which the user can visuallyinspect the size of the dose being set by rotating the dose settingbutton 4.

FIG. 2 discloses the injection device 1 with the cap 2 removed. In thismode, the user can inspect the drug contained in the injection devicethrough the inspection opening 6. The shield 20 is in its retractedposition and the user has full access to the connecting means 31provided distally on the needle holder 30.

In this mode the axial movement of the shield 20 in the distal directionis hindered by two flexible arms 32 provided on the needle holder 30 andshown in details on FIG. 12-13. These flexible arms 32 are provided inconjunction with the connecting means 31 such that once an injectionneedle 100 is connected to the connection means 31, this injectionneedle 100 pushes the flexible arms 32 inwardly to allow passage of theaxial movable shield 20 in the distal direction.

In FIG. 3, the user has attached an injection needle 100 to theconnecting means 31. The injection needle 100 is a conventional penneedle 100 (see FIG. 12) comprising a hub 102 to which a metallic needlecannula 101 is secured. The needle cannula 101 has a distal end 103 forpenetrating the skin of a user and a proximal end 104 for entering intoa cartridge 105 contained in the injection device 1.

When a user dials a dose by rotating the dose setting button 4(indicated by the arrow S in FIG. 4), the shield 20 is automaticallymoved into its extended position as disclosed in FIG. 4. In thisextended position the shield 20 visually covers the distal end 103 ofthe needle cannula 101, at least when the injection device 1 is viewedradially i.e. when vied from the side.

An injection is hereafter performed simply by pressing the distal end ofthe shield 20 softly against the skin of the user. This is indicatedwith the arrow I in FIG. 5. The distal part 103 of the needle cannula101 penetrates through the skin of the user, and the shield 20 whenmoving into its retracted position automatically activates the injectionof the set dose as will be explained later.

Following injection, when the distal end 103 of the needle cannula 101is removed from the skin of the user as disclosed in FIG. 6, the shield20 is maintained in its retracted position and the needle holder 30moves axially into its extended position making it possible for the userto exchange the injection needle 100.

The various sequences of an injection are schematically disclosed inFIG. 7. The details will be further explained in the following.

In FIG. 7.1, the cap 2 has been removed and the injection needle 100 hasbeen connected to the connection means 31 of the needle holder 30. Nodose has been dialled as can be seen in the window 5.

In FIG. 7.2 the user dials a dose, and the shield 20 is moved forward tocover the distal end 103 of the injection needle 101.

In FIG. 7.3 the shield 20 is pressed against the skin S of a user.

In FIG. 7.4, the distal end 103 of the needle cannula 101 has penetratedthrough the skin S of the user and the needle holder 30 and the shield20 locks to each other and moves axially together as further disclosedin FIG. 15.

In FIG. 7.5, the proximal end 104 of the needle cannula 101 haspenetrated through the septum 106 of the cartridge 105. The injectionitself is being executed in this position, indicated by the number “0”appearing in the window 5. Once the scale drum in returned to zero itlocks the shield to the housing (via the scale drum).

In FIG. 7.6 the needle holder 30 is forced forward which decouples theproximal end 104 of the needle cannula 101 from the cartridge 105.

In FIG. 7.7 this decoupling is fulfilled and in FIG. 7.8 the needleholder 30 locks to the housing 3.

FIRST EXAMPLE

The operation of the injection device 1 according to a first examplewill be explained in details in conjunction with the FIGS. 8 to 18.

The mechanics of the injection device 1 is contained in an outer housing3, which is preferably made from two parts, a distal cartridge holder 3a which is permanently secured to a proximal housing part 3 b to formone housing 3. An intermediate part 7 carrying a partition 8 is providedbetween the cartridge holder 3 a and the proximal housing part 3 b.Alternatively the housing 3 can be formed as one unitary unit.

As identified before, the distal end of the housing 3 carries a shield20 and a needle holder 30 whereas the proximal end of the housing 3carries the dose setting button 4.

The distal cartridge holder part 3 a further stores the cartridge 105which is a conventional cartridge 105 having a septum 106 at its distalend and an axially movable plunger 107 slidable provided at its proximalend. By moving the plunger 107 in the distal direction, the volume ofthe area between the septum 106 and the plunger 107 is reduced with thevolume being pressed out through the needle cannula 101 of the injectionneedle 100.

The cartridge 105 is axially locked to the housing 3. The proximal end109 of the cartridge 105 abuts the partition 8 as disclosed in FIG.10-11 and the shoulders 108 of the cartridge 105 abut inwardly pointingprotrusions 9 internally in the housing 3 such that the cartridge 105cannot slide axially in relation to the housing 3. In order to obtainthe tolerances of the cartridge a number of distally pointing fingers 12can be provided on the partition 8. These fingers 12 preferably has asloping surface to press against the proximal end 109 of the cartridge105 as disclosed in FIG. 11. The inwardly pointing protrusions 9securing the cartridge 105 distally can be provided at a distal end ofthe opening 6, they could however be provided wherever needed.Alternatively the cartridge 105 can be moulded to the housing 3.

In order to move the plunger 107 forward a drive mechanism is providedwhich mechanism comprises a threaded piston rod 40 which at its distalend presses against the plunger 107 preferably with a washer 43 providedbetween the piston rod 40 and the plunger 107.

The intermediate housing part 7 with its internal partition 8 isinrotatable secured to the housing 3 preferably between the two housingparts 3 a, 3 b. The intermediate housing part 7 could alternatively bemoulded as an integral part of the housing 3. The outside thread 41 ofthe piston rod 40 engages an internal thread 10 provided centrally inthe intermediate housing part 7 such that whenever the piston rod 40 isrotated it moves axially in relation to the intermediate housing part 7a distance determined by the number of revolutions of the piston rod 40and the pitch of the threads 10, 41.

The piston rod 40 is further provided with an axial stretching track 42which is engaged by a piston rod guide 50 such that whenever the pistonrod guide 50 rotate, the piston rod 40 rotates simultaneously and isscrewed forward in the thread connection 10/41.

The needle holder 30 is as disclosed in FIG. 12-13 provided with anumber of flexible arms 32 which are pressed outwardly by the inherentforce of the flexible arms 32. In this outwardly pointing position, theflexible arms 32 abuts the shield 20 in a pair of grooves 21 provided ona flange 22 of the shield 20 such that the shield 20 is prevented frommoving distally relatively to the needle mount 30, as indicated in FIG.2. In this position a user can mount the injection needle 100 to theconnection means 31. When the injection needle 100 is mounted onto theconnecting means 31, the flexible arms 32 will bend and be brought intoalignment with the outside surface of the connecting means 31 of theneedle holder 30 and the shield 20 can slide freely relatively to theneedle mount 30 as depictured in FIG. 13.

In order to visually indicate the size of the dose being set by rotatingthe dose setting button 4 a scale drum 60 is provided. The scale drum 60is provided with an external thread 61 engaging a similar threadprovided internally in the housing 3 as seen in FIG. 10.

The dose setting button 4 engages the drive tube 70 at its proximal endvia a ratchet mechanism which is described in details in the not yetpublished PCT/EP 2013/055403 to Novo Nordisk NS, which is herebyincorporated by reference. This ratchet mechanism as disclosed in FIG.17 comprises a spring base 80 which is permanently secured to thehousing 3 and has an internal toothing engaging the ratchet arms 86 ofthe ratchet element 85.

The ratchet element 85 is further provided with an internal toothing 87engaging a similar toothing 71 externally provided on the drive tube 70such whenever a user rotates the dose setting button 4 to set a dose,the dose setting button 4 rotates the ratchet element 85 and togetherwith it the drive tube 70.

The dose setting button 4 engages directly with the ratchet element 85which rotates together with the dose setting button 4 both when settinga dose and when lowering the set dose by rotating the dose settingbutton 4 in the opposite direction. The dose setting button 4 furtherhas an internally provided protrusion which is able to move the ratchetarm 86 out of engagement with the internal toothing of the spring base80 when the dose is being lowered.

A torsion spring A is provided between the drive tube 70 and the springbase 80, which torsion spring A is strained whenever the drive tube 70is rotated in the dose setting direction. The spring base 80 couldalternatively be a part of the housing 3 in which case the torsionspring A would be encompassed between the housing 3 and the drive tube70.

Besides the torsion spring A delivering the torsional force to performthe injection, two other springs are provided. A helical spring Bapplying an axial force is provided between a flange 28 on the shield 20and the internal partition 8 of the intermediate part 7 of the housing 3urging the shield 20 in the distal direction and a second axiallyworking helical spring C is provided between a flange 33 provideddistally on the needle mount 30 and the housing 3 urging the needlemount 30 in the distal direction. The helical spring C can rest againstthe distal side of the internal protrusions 9 inside the housing part 3a securing the cartridge 105 as disclosed in FIG. 8.

The drive tube 70 is on an outside surface provided with an axial groove72 being engaged by a corresponding raised bar 62 internally in thescale drum 60, such that the scale drum 60 follows rotation of the drivetube 70 and can move axially in relation to the drive tube 70. Since thescale drum 60 is threaded to the housing 3 it performs a helicalmovement whenever rotated. Externally the scale drum 60 is provided witha series of indicia indicating the size of the dose which indicia can beviewed through the window 5 in the housing 3.

As disclosed in FIGS. 10-11, the distal end the scale drum 60 isinternally provided with hooks 63 engaging similar indentations 23provided proximally on a pair of identical arms 24 a,b providedproximally on the shield 20.

The shield 20 is urged in the distal direction by the helical spring Bwhich is encompassed between the partition 8 of the intermediate housingpart 7 and the shield 20 thus applying a distally orientated force onthe shield 20. The shield 20 is further provided with an axial surface25 which is guided by a similar axial surface 11 provided along theinspection opening 6 inside the housing 3 such that the shield 20 isguided solely axially without the possibility of rotating relatively tothe housing 3.

Whenever the scale drum 60 is in its most distal position, the hooks 63will engage the indentations 23 on the shield 20 and thus prevent thehelical spring B form urging the shield 20 in the distal direction (FIG.10), however when the scale drum 60 is rotated to set a dose asdisclosed in FIG. 11, the indentations 23 are released from the hooks 63and the shield 20 travels in the distal direction under the forceapplied by the helical spring B. Thus, when a user dials a dose asdepictured in FIG. 4 (arrow D), the shield 20 is released to move in thedistal direction to cover the distal end 103 of the needle cannula 101.

End-of-Content

An end of content mechanism disclosed in FIG. 17 comprises an EOC tube45 and an EOC ring 55. The EOC ring 55 carries an outside thread 56which is threaded inside the EOC tube 45 and is axially guided on thedrive tube 70 by having an internal protrusion 57 guided in an axialtrack 73 on the drive tube 70.

Further the EOC tube 45 has an internal flange 49 which is captured byhooks 75 provided on the drive tube 70 allowing the EOC tube 45 to slidea short distance axially in relation to the drive tube 70.

Whenever a dose is set, the drive tube 70 is rotated and the EOC tube 45is held inrotatable by having teeth 46 engaging similar teeth inside thespring base 80. The EOC ring 55 is thereby dialled up the EOC tube 45 adistance which relates to the size of the set dose. During expelling ofthe dose, the drive tube 70 is moved axially in relation to the EOC tube45 as will be explained later, the result being that the distal toothing47 on the EOC tube engages a similar toothing in the drive tube 70 suchthat the drive tube 70 and the EOC tube 45 rotates simultaneously duringdosing whereby the EOC ring 55 remains in its relative position. Theposition of the EOC ring 55 in the internal thread of the EOC tube 45 istherefore an expression of the accumulated set doses.

The helical length of the internal thread of the EOC tube is made suchthat the EOC ring 55 reaches the end of the internal thread of EOC tube45 when the cartridge 105 is empty, or at least empty for its usablecontent. At this point the EOC ring 55 abuts the end of the internalthread and prevents further rotation of the drive tube 70, thus nofurther dose can be set.

The EOC tube 45 can further be provided with teeth 48 engaging similarteeth in the spring base 80 providing dose clicks as the EOC tube 45rotates with the drive tube 70 during dosing.

Dose Setting

When a user sets a dose by rotating the dose dial button 4 as indicatedin FIG. 4, the rotation of the dose setting button 4 causes the ratchetelement 85 to also rotate. This rotation is transferred to the drivetube 70 via the toothing 71, 87.

As the drive tube 70 is rotated the torsion spring A encompassed betweenthe spring base 80 and the drive tube 70 is strained. The torsionthereby being built up in the torsion spring A is held by the ratchetarms 86 engaging the internal toothing of the spring base 80. Theratchet arms 86 can be actively released in order to dial down the sizeof the set dose.

As the drive tube 70 is rotated, the scale drum 60 rotate and movehelically thus indicating the size of the set dose in the window 5.

As the scale drum 60 starts to rotate, the hooks 63 of the scale drum 60moves out of the engagement with the indentations 23 of the shield 20which is then free to move axially under the influence of the helicalspring B. The shield 20 thus moves to a position covering the distal end103 of the needle cannula 101 as depictured in FIG. 4.

Once the user has set the size of the dose to be injected, the injectiondevice 1 is set and ready to perform an injection.

Activation

In order to release the torque applied to the torsion spring A andthereby to perform an injection, the shield 20 is pressed against theskin of the user as indicated by the arrow I in FIG. 5 which willtrigger the injection as explained below.

The needle holder 30 is provided with an identical set of flexible arms34 a,b. These arms 34 a,b are blocked in the axial direction by aninternal flange 13 provided inside the housing 3 as disclosed in FIG.14-16.

Further, the shield 20 is provided with two identical arms 24 a,bcarrying the indentations 23. These arms 24 a,b are each furtherprovided with a protrusion 26 as best seen in FIG. 16. As the shield 20travels in the proximal direction, this protrusion 26 presses theflexible arms 34 a,b inwardly such that the flexible arms 34 a,b, canslide under the internal flange 13 of the housing 3 as in FIG. 14 andthus allow the needle shield 30 to slide axially.

The needle holder 30 is further provided with a second pair of identicalarms 35 a,b. These arms 35 a,b carries proximally an extension 36.

The arms 24 a,b of the shield 20 each carry a radial protrusion 27 whichperipherally follows the outside surface of the cartridge 105. As theshield 20 is moved axially in the proximal direction, the radialprotrusions 27 abuts the extension 36 and further axial movement of theshield 20 will thus force the needle holder 30 to move along with theshield 10 in the proximal direction as the arms 34 a,b in this positionis able to escape under the flange 13.

As both the shield 20 and the needle holder 30 slides in the proximaldirection, the proximal end 104 of the needle cannula 101 penetratesthrough the septum 106 of the cartridge 105 since the cartridge 105which proximally rest against the partition 8 of the intermediate part 7is prevented from axial movement.

Dose Release

Once the proximal end 104 of the needle cannula 101 has penetratedthrough the septum 106 of the cartridge 105 and the distal end 102 haspenetrated through the skin of the user, the set dose is released in thefollowing manner.

The axial track of the piston rod 40 is engaged by the piston rod guide50 as disclosed in FIG. 16. The piston rod guide 50 is further providedwith an external toothing 51 (see e.g. FIG. 11) engaging a similartoothing 74 internally in the drive tube 70. The drive tube 70 and thepiston rod guide 50 can slide axially relatively such they can shiftbetween a position in which the toothing 74 of the drive tube 70 engageswith the toothing 51 of the piston rod guide 50 such that the piston rodguide 50 follows the rotation of the drive tube 70 and a position inwhich the drive tube 70 and the piston rod guide 50 is disengaged.

Distally, the piston rod guide 50 is engaged by the activator 90.

The activator 90 has a central part 91 which engages the piston rodguide 50 such that the activator 90 can move the piston rod guide 50axially while the piston rod guide 50 can rotate relatively to theactivator 90. Distally, the activator is provided with two identicallegs 92 a,b.

During activation as the needle holder 30 is moved in the proximaldirection by the shield 20, the proximal end of the arms 34 a,b abutsthe arms 92 a,b of the activator 90 and slides the activator 90 in theproximal direction.

This axial movement of the activator 90 pushes the piston rod guide 50into engagement with the drive tube 70.

The central part 91 of the activator 90 is provided proximally from thiswall partition 8 and the legs 92 a,b, extend through openings in thepartition 8. The partition 8 is further provided with a toothing 14(FIG. 8) which engages a similar toothing 53 internally in the pistonrod guide 50 such that the piston rod guide 50 is prevented fromrotation relatively to the partition 8 (and the housing 3) as long asthe piston rod guide 50 axially abuts the partition 8.

As the arms 34 a,b axially moves the piston rod guide 50 out ofengagement with the toothing 14 of the partition 8 and into engagementwith the drive tube 70 it also moves the drive tube 70 slightly in theproximal direction. This axial movement of the drive tube 70 moves theproximal toothing 71 of the drive tube 70 out of its engagement with theinternal toothing 87 of the ratchet 85 as shown in FIG. 17. As theratchet element 85 prevents the torque of the torsion spring A frombeing released, the torsion spring A is now able to rotate the drivetube 70 which rotates with it the piston rod guide 50 and thereby thepiston rod 40 to perform an ejection of the liquid drug.

After Dosing

Due to the engagement between the axial groove 72 of the drive tube 70and the raised bar 62 of the scale drum 60, the scale drum 60 rotatesback to its zero position during injection. As the scale drum 60 returnsto its zero position as shown in FIG. 18, the raised bar 62 engages anaxial surface 93 provided externally on the activator 90. The impact ofthe scale drum 60 with the activator 90 makes the activator 90 rotate anangle. This rotation makes the arms 92 a,b of the activator 90 moveunder a peripheral extension 36 e provided peripheral on the extension36 which lifts the extension 36 and thereby the proximal end of the arms35 a,b over the radial protrusion 27. In order to enhance this lifting,both the arms 92 a,b and the extension 36 e are preferably provided withan inclined surface as depictured in FIG. 18. The helical spring Curging an axial force on the needle holder 30 now pushes the needleholder 30 in the distal direction such that the proximal end 104 of theneedle cannula 101 is moved out of its engagement with the septum 106 ofthe cartridge 105. When setting a dose the activator 90 is rotated backto its initial position.

The needle shield 20 is in the zero position locked to the scale drum 60due to the engagement 63/23 and is thus hindered from moving axially.The result being as shown in FIG. 6, that the needle shield 20 remainsin its retracted position and the needle holder 30 moves into its mostdistal position thereby making it possible for the user to exchange theinjection needle 100

SECOND EXAMPLE

A second example which essentially works the same way as the firstexample is disclosed in the FIGS. 19-26.

Whenever possible the individual elements of the second example arenumbered with the same number as in the first example, however, havingthe number “1” or “10” in front. The same apply for elements performingthe same or similar activity.

As in FIG. 9 the second example is disclosed in an exploded view in FIG.20.

As disclosed the housing 1003 is made up from three housing parts; adistal cartridge holder part 1003 a holding a cartridge 1105, a proximalhousing part 1003 b which at its most proximal end is provided with adose setting button 1004 and an intermediate housing part 1007connecting the cartridge part 1003 a and the proximal housing part 1003b. The cartridge holder part 1003 a is further, in the non-usesituation, covered by a removable cap 1002.

The intermediate housing part 1007 is further provided with a distalextension 115 which will be explained later and a proximal extension116. The proximal extension 116 has at its most proximal end a pointerwhich will appear in the scale window 1005 when the housing 1003 isassembled (best seen in FIG. 21-22). Further, the proximal extension 116can carry an inwardly pointing thread segment 117 for engaging theexternal thread 161 on the scale drum 160.

The proximal housing part 1003 a is provided with two opposite locatedopenings 1006 (one of which is depictured in FIG. 20) into which twoframes 111 are press fitted. One or both of these frames 111 areinternally provided with a holding mechanism 1009 for holding the neckpart 1108 of the cartridge 1105. The proximal end 1109 of the cartridge1105 is secured against the partition 1008 of the intermediate part 1007such that the cartridge 1105 is fixed in the housing 1003.

Movable relatively to the housing 1003 is the shield 120 which cover theinjection needle during injection and the needle holder 130 havingconnecting means 131 for securing an injection needle to the needleholder 130. The needle holder 130 is further provided with a flexiblearm 132 preventing proximal movement of the shield 120 relatively to theneedle holder 130 when no injection needle is mounted on the needleholder 130.

Further, a torsion spring A supplies the torque for performing aninjection whereas a compression spring B urges the shield 120 in thedistal direction and another compression spring C urges the needleholder 130 in the distal direction.

The torsion spring A is encompassed between the spring base 180 and thedrive tube 170. The spring base 180 is permanently fixed to the proximalhousing part 1003 b but could alternatively be moulded as an integralpart of the housing 1003.

The compression spring B is encompassed between a flange (or similar)128 on the shield 120 and the internal partition 1008 of theintermediate housing part 1007. The flange 128 could alternatively be anumber of knobs supporting the spring B.

The compression spring C is made from a suitable polymer and is mouldedas an integral part of the needle holder 130 and encompassed between theneedle holder 130 and the partition 1008 of the intermediate housingpart 1007. The partition 1008 can e.g. be provided with a hole 114 forsecuring the moulded compression spring C.

The intermediate housing part 1007 further has an internal thread 110through which the piston rod 140 is screwed forward when rotated.

A scale drum 160 for showing the size of the set dose is via an outsidethread 161 threaded to the proximal housing part 1003 b or to thethreaded segment 117 of the proximal extension 116 of the intermediatehousing part 1007 (or it can be threaded to both as a security measure)such that the scale drum 160 moves helically when rotated. Internallythe scale drum 160 is provided with a raised bar 162 axially guided in acorresponding axial groove or the like 172 provided externally on thedrive tube 170. The raised bar 162 and axial groove 172 engagement couldof cause be vice versa in respect of the parts.

The scale drum 160 is further provided with a hook 163 which holds theshield 120 in its retraced position when the scale drum 160 is in itsmost distal position i.e. when no dose is set.

The proximally provided dose setting button 1004 is internally rotatableconnected to the ratchet element 185 such that rotation of the dosesetting button 104 is transformed into rotation of the ratchet element185. The ratchet element 185 is urged in the distal direction by acompression spring D provided between the proximal end of the ratchetelement 185 and the dose setting button 1004. This spring D ispreferably moulded integrally with the ratchet element 185 as depicturedin FIG. 19. The dose setting button 1004 is further rotatable connectedto the housing 1003 such that it can rotate relative to the proximalhousing part 1003 b but not move axially.

The ratchet element 185 is further provided with a ratchet arm 186 whichengages an internally toothing 181 provided internally in the springbase 180. The engagement of the ratchet arm 186 with the internaltoothing 181 prevents the ratchet element 185 from counter rotating.However, the dose setting button 1004 is internally provided with aprotrusion 1010 (FIG. 19) which can move the ratchet arm 186 inwardlywhen the dose setting button 1004 is rotated oppositely to lower the setdose. In this way the ratchet element 185 can rotate step by step in theopposite direction during dial-down of the dose and under influence ofthe torsion spring A.

Dose Setting

When setting a dose, as depictured in FIG. 21, the user simply rotatesthe dose setting button 1004 which in turn rotates the ratchet element185. Rotation of the ratchet element 185 is transferred to a rotation ofthe drive tube 170 as the inner toothed surface 174 of the drive tube170 is in engagement with the outer tooting 187 provided on the ratchetelement 185. The rotation of the drive tube 170 strains the torsionspring A. The torque build up in the torsion spring A is held by theengagement of the ratchet arm 186 with the internal toothing 181 of thespring base 180.

The scale drum 160 rotates together with the drive tube 170 such thatthe user can view the set dose through the window 105 provided in theproximal housing part 103 b.

Once the scale drum 160 is rotated away from its “zero” position thehook 163 is rotated out of its engagement with the indentation 123 (seeFIG. 23-26) provided on the shield 120 which is then urged distally bythe compression spring B.

The needle holder 130 is further urged forward by the compression springC such that the back-end of the injection needle is maintained outsidethe septum 1106 of the cartridge 1105 when not injecting.

Injecting

In order to inject the set dose, the distal end of the shield 120 ispressed against the skin of the user.

When the user starts to press the shield 120 against the skin, thefront-end 103 of the injection needle 100 penetrates through the skinwhile the back-end 104 of the injection needle is out of contact withthe septum 1106 of the cartridge 1105 as the needle holder 130 is in itsdistal position. In this position, the needle holder 130 is preventedfrom moving proximally by the engagement of the protrusion 134 a carriedon the flexible arm 134 against an inwardly pointing protrusion 113 (seeFIG. 20) provided on the frame 111.

However, once the front-end 103 of the injection needle 100 is fullyinserted into the skin as depictured in FIG. 7.4, the shield 120 willforce the protrusion 134 a out of its engagement with the inwardlypointing protrusions 113 of the frame 111 since the vertical protrusion134 b of the flexible arm 134 is guided in a track 126 in the shield120. The shape of this track 126 moves the protrusion 134 a (via 134 b)out of its engagement with the inwardly pointing protrusion 113 on theframe 111 where after the shield 120 and the needle holder 130 moveaxially together.

The shield 120 and needle holder 130 moves together since the protrusion136 provided on the arm 135 locks to the hook 127 proximally provided onthe shield 120. Axial movement of the shield 120 is thus transferred tothe needle holder 130. This is best seen in FIG. 23-24 which depicturesthe situation occurring during dose expelling and just before the scaledrum 160 reaches its zero position. The hook 127 engages the protrusion136 thus transferring axial movement of the shield 120 to axial movementof the needle holder 130.

The arm 135 carrying the protrusion 136 is guided into position by thecurved wall 129 leading up to the hook 127. Oppositely the arm 135 issupported by the curved extension 115 on the intermediate housing part1007.

When the shield 120 is fully retracted, as depictured in FIG. 7.5, theback-end 104 of the injection needle 100 has penetrated through theseptum 1106 and into the cartridge 1105 and the release of the dose willbe activated.

Dose Release

Proximally on the needled holder 130 one or more release arms 137 areprovided. These release arms 137 extent parallel with the flexible arm135. When the shield 120 and the needle holder 130 is in their proximalposition, the release arms 137 moves the clutch 190 as depictured inFIG. 22. This brings the external toothing 191 on the clutch 190 intoengagement with a similar toothing 174 provided internally in the drivetube 170 such that the drive tube 170 and the clutch 190 rotatetogether.

During dose setting, the ratchet element 185 rotates the drive tube 170via the engagement of the externally provided toothing 187 engaging thetoothing 174 internally in the drive tube 170, see FIG. 21.

Further, during dose setting, the ratchet element 185 rotate togetherwith the dose setting button 1004, but during dosing both the dosesetting button 1004 and the ratchet element 185 remains non-rotatable.When the clutch 190 is moved proximally by the arms 137, the ratchetelement 185 is also moved proximally against the bias of a proximallymoulded spring arm D provided proximally on the ratchet element 185 andresting against an inside surface of the dose setting button 1004.

This proximal movement of the ratchet element 185 releases the couplingbetween the toothing 174 of the drive tube 170 and the toothing 187provided on the ratchet element 185 such that the drive tube 170 is freeto rotate under influence of the torque of the torsion spring A.

The rotation of the drive tube 170 is transferred to a rotation of theclutch 190 by the coupling between the internal toothing 174 on thedrive tube 170 and the toothing 191 externally and proximally on theclutch 190.

I.e. when the clutch 190 slides proximally (moves from the position inFIG. 21 to the position of FIG. 22) the toothing 174 of the drive tube170 releases the engagement with the toothing 187 of the ratchet element185 and couples to the toothing 191 of the clutch 190.

A further toothing 171 is also provided internally in drive tube 170,which toothing 171 operates against click arms 188 provided externallyon the ratchet element 185 to provide dose clicks during injection i.e.when the drive tube 170 rotate relatively to the ratchet element 185.

Please note that in the FIGS. 21-22 part of the clutch 190 is notvisible due to the cross sectional view. However, the clutch 190 isfully depictured in FIG. 19

Further, the rotation of the clutch 190 is transferred to a rotation ofthe piston rod guide 150 as the toothed outer surface 151 of the pistonrod guide 150 is in engagement with the internal toothing 194 of theclutch 190 when the clutch 190 is moved proximally during dosing asdisclosed in FIG. 22.

As seen in FIG. 21-22 this internal toothing 194 of the clutch 190 is inengagement with a toothing 118 on the intermediate housing member 1007when the injection device is not activated.

The rotation of the piston rod guide 150 is transferred to a rotation ofthe piston rod 140 as the piston rod guide 150 engages a longitudinaltrack in the piston rod 140.

Pressure Relief

The pressure relief mechanism is similar to the one disclosed in EP12-188471 by Novo Nordisk NS and serves the purpose of allowing axialmovement of the rubber plunger 1107 of the cartridge 1105 and thus alsoof the piston rod 140. Such axial movement of the rubber plunger occurse.g. as a result of temperature variations.

The pressure relief mechanism comprises of the clutch 190, the pistonrod guide 150, a click element 165 and a leaf spring E.

If the liquid drug inside the cartridge 1105 expands due to increasingtemperatures, the piston rod 140 will be forced proximally by the rubberplunger 1107 inside the cartridge 1105, which will push the piston rodfoot 143 and thus the piston rod 140 proximally. This will generate arotation of the piston rod 140 as the piston rod 140 is threaded to thethread 1008 of the intermediate part 1007.

This will force the piston rod guide 150 to rotate as the piston rodguide 150 is keyed to the piston rod 140.

The click element 165 is externally provided with a plurality of clickfingers 166 which operates in a toothing 195 provided internally in theclutch 190. This toothing 195 is adapted to prevent rotation of theclick element 165 in one direction and adapted to have reluctance torotation in the opposite direction (due to the inherent outwardlyflexibility of the click fingers 166).

The direction having the reluctance is the one being used when thepiston rod 140 move proximally as the temperature rises.

The leaf spring E is encompassed between the piston rod guide 150 andthe click element 155 such that one leg of the leaf spring D is attachedto the piston rod guide 150 and the other leg is attached to the clickelement 165 thus a torque will be introduced in the leaf spring E whenthe piston rod guide 150 and the click element 165 rotate relative toeach other independently of the direction of this rotation.

When the piston rod 140 move proximately and the piston rod guide 150rotates, the leaf spring E is tighten until the rotational reluctance ofthe click element 165 is overcome where after the click fingers 166 willmove to the subsequent teeth of the toothing 195. The result being thatthe piston rod guide 150 can perform an unlimited rotation in theexpanding direction.

When the temperature decreases and the rubber plunger move distally thetorque introduced in the leaf spring E will rotate the piston rod guide150 since the toothing 195 prevents the click element 165 from rotationin this opposite direction. The result being that the piston rod 140 isrotated forward.

End-of-Content

The End-of-Content mechanism is a so-called non-axial movable cycloidEnd-of-Content mechanism which is disclosed in details in EP 13-153628by Novo Nordisk NS.

The End-of-Content mechanism comprises an End-of-Content ring 155 whichinternally rides on an outside surface of the clutch 190 and externallyis connected to a toothed ring 175 provided inside drive tube 170 suchthat the End-of-Content ring 155 rotate when the drive tube 170 isrotated relatively to the clutch 190.

During dose setting the drive tube 170 is rotated and the clutch 190 isstatic thus the End-on-Content ring 155 is rotated. During dosing thedrive tube 170 and the clutch 190 rotate together thus maintaining theEnd-of-Content ring 155 in the same relative position.

Due to the cycloid gearing the End-of-Content ring 155 is rotated agreater angle for each angular rotation of the drive tube 170 therebycounting the rotational movement of the drive tube 170. The totalallowable angular movement of the End-of-Content ring 155 ispredetermined such that the End-of-Content ring 155 encounters a stopjust before the injectable content of the cartridge 1105 has been set.Once the End-of-Content ring 155 reaches its stop, the drive tube 170cannot be rotated further thus no further dose can be set.

The End-of-Content mechanism thereby counting the accumulated set andejected doses and stopping further dose setting when this accumulatedvalue equals the initial injectable amount of liquid drug in thecartridge 1105.

After Dosing

Following dose release the user removes the shield 120 from the skin asdisclosed in FIG. 7.8.

This makes the needle holder 130 move distally under the influence ofthe compression spring C as depictured in FIG. 23-24 such that theback-end 104 of the attached pen-needle 100 is pulled out of the septum1106 of the cartridge 1105.

As the scale drum 160 approaches its zero position as depictured in FIG.23-24, the surface 164 on the scale drum 160 encounters the protrusion136 and pushes it out of its engagement with the hook 127 such that theneedle holder 130 can move distally independently of the shield 120.

To make sure that the needle holder 130 do not return until the shield120 has been fully removed from the skin of the user, the protrusion 136is hindered by axial movement by the supporting surface 115 until theshield 120 has moved a little distance in the distal direction (thedistance is indicated by the arrow Z in FIG. 23). The axial movementbeing the axial distance Z between hook 163 and indentation 123 seen inFIG. 23. Only when the shield 120 has moved to the hooked position (FIG.25) is the distance to the supporting surface 115 sufficient to allowthe protrusion 136 to be fully released where after the needle holder130 returns to its extended position.

Also following injection, the hook 163 provided on the scale drum 160once again engages the indentation 123 provided proximately on theshield 120 thus preventing further axial movement of the shield 120 asdepictured in FIG. 24-25.

This mechanism is further disclosed in European patent application No.:EP 13-170422 by Novo Nordisk NS.

Some preferred embodiments have been shown in the foregoing, but itshould be stressed that the invention is not limited to these, but maybe embodied in other ways within the subject matter defined in thefollowing claims

1. A spring driven drug delivery device for delivering set doses of aliquid drug comprising: a housing securing a cartridge containing theliquid drug and which cartridge is axially fixated to the housing, adose setting arrangement for setting the size of the dose to bedelivered, a torque spring drive mechanism for automatically driving theset dose out from the cartridge through an exchangeable injection needlemountable to the drug delivery device, the torque spring drive mechanismcomprising a piston rod which is axially displaceable through engagementwith a rotational piston rod guide rotational under the influence of atorsion spring, a telescopically movable needle shield for covering adistal end of the attached injection needle in an extended position andwhich needle shield when axially moved to a retracted position triggersthe release of at least a portion of the torque of the torsion spring inorder to perform an ejection of the liquid drug, and wherein a needleholder for carrying the exchangeable injection needle is axially movablerelatively to both the housing and to the needle shield.
 2. A springdriven drug delivery device according to claim 1, wherein the torsionspring is encompassed between the housing and the piston rod guide.
 3. Aspring driven drug delivery device according to claim 2, wherein a drivetube is rotatable during dose expelling and which drive tube rotates thepiston rod guide.
 4. A spring driven drug delivery device according toclaim 3, wherein a clutch couples the drive tube to the piston rod guideduring dose expelling.
 5. A spring driven drug delivery device accordingto claim 4, wherein the clutch is movable between a first position inwhich the clutch is rotational locked to the housing and a secondposition in which the clutch is rotational released from the housing androtational coupled to the drive tube and to the piston rod guide suchthat the torque of the torsion spring is transformed into a rotation ofthe piston rod guide in the second position.
 6. A spring driven drugdelivery device according to claim 1, wherein the needle shield ismovable from the retracted position to the extended position under theinfluence of a helical compression spring provided between the housingand the needle shield upon activation of a dose setting button of thedose setting arrangement.
 7. A spring driven drug delivery deviceaccording to claim 6, wherein the dose setting arrangement upon rotationof the dose setting button is adapted to rotate a scale drum which isthreadedly engaged with the housing to perform a helical movement andwhich scale drum engages and locks the needle shield when in a zeroposition.
 8. A spring driven drug delivery device according to claim 7,wherein hooks or the like formed on the needle shield engagescooperating hooks provided on the scale drum in the retracted position.9. A spring driven drug delivery device according to claim 1, whereinthe needle shield is slidable on an outside surface of the needle holderand which needle holder is provided with a number of flexible armsprojecting from an outside surface of the needle holder and engaging theneedle shield.
 10. A spring driven drug delivery device according toclaim 1, wherein the needle shield when moved from its extended positionto its retracted position abuts and moves the needle holder axially. 11.A spring driven drug delivery device according to claim 10, wherein theneedle shield has a number of protrusions which engages the needleholder to move the needle holder axially.
 12. A spring driven drugdelivery device according to claim 11, wherein one or more protrusioncarried by proximate extending arms provided on the needle holderengages the protrusions of the needle shield.
 13. A spring driven drugdelivery device according to claim 10, wherein the injection needlemoves axially together with the needle holder such that the proximal endof the injection needle penetrates a septum in the cartridge therebyallowing the liquid drug to flow through the injection needle.
 14. Aspring driven drug delivery device according to claim 10, wherein theaxial and proximally movement of the needle holder moves the clutch fromits first position to its second position thereby activating the releaseof the torsion spring to drive the torque spring drive mechanism.
 15. Aspring driven drug delivery device according to claim 8, wherein thescale drum rotates back to its zero position during expelling of the setdose under influence of the torsion spring.
 16. A spring driven drugdelivery device according to claim 15, wherein the scale drum when itreaches its zero position following injection releases the needle holdersuch that the needle holder move axially in the distal direction underinfluence of a helical compression spring provided between the needleholder and the housing.
 17. A spring driven drug delivery deviceaccording to claim 16, wherein the scale drum abuts the protrusion ofthe needle holder to release the needle holder to move axially.
 18. Aspring driven drug delivery device for delivering set doses of a liquiddrug comprising: a housing fixating a cartridge containing the liquiddrug to be injected, a needle holder to which an injection needle ismountable, a needle shield for covering the injection needle during use,wherein, the needle shield is axially slidable relatively to the needleholder and which needle holder is provided with a number of flexiblearms preventing axial movement of the needle shield when no injectionneedle is mounted on the needle shield and which arms are activated andmovable into alignment with the needle holder when an injection needleis mounted on the needle holder thereby allowing the needle shield tomove axially relatively to the needle holder.
 19. A spring driven drugdelivery device for delivering set doses of a liquid drug comprising: ahousing fixating a cartridge containing the liquid drug to be injected,a scale drum threadely engaged with the housing to perform a helicalmovement away from a zero position during setting of a dose, a needleshield for covering the injection needle during use, which needle shieldis axially slidable in relation to the housing, and wherein the scaledrum engages and locks the needle shield from axial movement when in thezero position.
 20. A spring driven drug delivery device for deliveringset doses of a liquid drug comprising: a housing fixating a cartridgecontaining the liquid drug to be injected, a needle holder to which aninjection needle is mountable and which needle holder is axiallyslidable in relation to the housing, a needle shield for covering theinjection needle during use and which needle shield is axially slidablein relation to the housing, wherein, the needle shield is slidablerelatively to the needle holder and which needle holder is provided witha number of flexible arms preventing axial movement of the needle shieldwhen no injection needle is mounted on the needle holder and which armsare activated and moved into alignment with the needle holder when aninjection needle is mounted on the needle holder thereby allowing theneedle shield to move axially relatively to the needle holder, andfurther comprising a scale drum threadely engaged with the housing toperform a helical movement away from a zero position during setting of adose wherein the scale drum engages and locks the needle shield fromaxial movement when in the zero position.